Having built the boards and test assembled I thought I'd check the results I'm getting are to be expected for the high power build:
-Supply voltages: +10.54v and -10.59v
-Voltage across R17 & R18 rising from 0.182 at switch on and settling at 0.207 which puts bias at around 93mA?
Heatsink temperatures measuring around 62-65 degrees C (ambient is 18)
-Supply voltages: +10.54v and -10.59v
-Voltage across R17 & R18 rising from 0.182 at switch on and settling at 0.207 which puts bias at around 93mA?
Heatsink temperatures measuring around 62-65 degrees C (ambient is 18)
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Hi @arfadow
Full disclosure: the high power build, which nominally doubles the bias current from 38 to 75 mA, was a paper build on my part, I calculated the values and confirmed with the help of the TLSpice simulation.
I (and TLSpice) neglected to consider the temperature increase. The high temps are changing the transistor properties leading to - not thermal runaway exactly - but an increase in bias current from ~80 mA to ~95 mA as the components warm up.
The solution involves replacing some resistors, moving the values back towards the 38 mA build. Let me dig out the simulation to give you your best option to dial it back a little.
That said +45 above ambient / 65C operating temps are reasonable, there is no particular reason not to use.
Full disclosure: the high power build, which nominally doubles the bias current from 38 to 75 mA, was a paper build on my part, I calculated the values and confirmed with the help of the TLSpice simulation.
I (and TLSpice) neglected to consider the temperature increase. The high temps are changing the transistor properties leading to - not thermal runaway exactly - but an increase in bias current from ~80 mA to ~95 mA as the components warm up.
The solution involves replacing some resistors, moving the values back towards the 38 mA build. Let me dig out the simulation to give you your best option to dial it back a little.
That said +45 above ambient / 65C operating temps are reasonable, there is no particular reason not to use.